The present invention relates to polymer compositions which are metallized, in particular with intermetallic compounds. The invention also relates to convenient processes for preparing such metallized polymer compositions. Furthermore, the invention relates to a process for producing electrically conductive films. Finally, the invention envisages advantageous uses of the processes.
In the development of currently available commercial processes of producing satisfactory metal-to-plastic bonding the plating of polymeric materials has met increasing interest and found widening applications. The replacement for metal articles by plastic items obviously offers the advantages of lower cost, higher production speed, wider design latitude, weight savings and fewer corrosion problems in view of the applicable extrusion and injection molding techniques, and the inherent properties of the polymeric materials. For many application purposes, however, a metallic coating on the polymeric article is desirable, since in that way the hardness, wear resistance, shiny appearance and metallic feel characteristic of metals is imparted to the polymeric substitutes. Furthermore, mention should be made of printed circuit boards which comprise dielectric substrates carrying metal electrical circuits. Finally the plating of plastic articles has found application in shielding electromagnetic interference (EMI) from electronic equipment. This EMI causes problems to advanced electronic devices of great sensitivity. Regulations concerning this new electronic pollution are or will be effective in USA and Europe.
Since most plastic surfaces are not electrically conductive, the traditional electroplating methods are not quite suitable for providing a metallic coating. Currently, however, electroless plating is one feasible method for the plating of polymeric materials. Though the development of chemical etchants resulting in a controlled microporous surface of the polymeric material and greatly improved electroless plating baths has led to metal depositions which adhere well to the polymeric surface and may serve as a conductive preplating for subsequent electroplating, all electroless plating processes are labor intensive, complicated and hence expensive. For example, a typical electroless plating procedure involves the steps of etching the polymeric material with strongly oxidizing solutions of chromic acid in order to physically roughen the polymeric surface and chemically modify it to give it a hydrophilic nature, neutralizing it with a mildly acidic or basic reducing agent for removing the detrimental hexavalent chromium, sensitizing it with stannous chloride and palladium chloride for nucleation of palladium, accelerating it with acidic or basic solutions for removing excess tin and exposing pallidium nuclei and electroless depositing metals such as nickel and copper on it from a plating bath.
A method for high-speed production of metal-clad articles is disclosed in the International Patent Application No. WO 02784, which method comprises electroplating the injection molding die surface prior to each molding operation of a plastic article and the transfer of the electrodeposit to the plastic surface as a result of the higher adhesion of the electrodeposit to the plastic article formed than to the surface of the mold member. This method, however, requires the preliminary formation of the metallic layer and subsequent bonding to the polymeric article during formation of the latter.
Further, it is known from GB Patent No. 1,309,320 that flammable plastics can be compounded with combinations of halogen containing low molecular weight compounds and antimony trioxide. It is stated therein that certain additives tend to effloresce through lack of compatibility with the plastics material, which over a period of time, can result in thick coatings being formed on the surfaces of molding or machine parts. The nature of such coatings, however, is not defined, and no use is mentioned.
From EP Patent Application No. 125,617 it is known to metallize polymer compositions by heat treatment of a composition of a polymer and an organic complex of a transition metal element. A metallized surface film was obtained when the heat treatment was conducted with the polymer composition being in initimate contact with a metallizing board, which had to be made of a material having adequate heat resistance and to be readily releasable from the metallized film. The metal layers obtained did not contain a main group element.
In U.S. Pat. No. 3,620,834 a method is disclosed for metal plating plastic materials, wherein a substrate is successively pretreated with a main group V element trichloride and a source of sulfide prior to electrodeposition of Ni or Cu by conventional techniques.
From German Patent Application No. 2,022,109 it is known to treat in the presence of a solvent the surface of a plastic article with a dissolved metal salt complex, such as SnC1.sub.2. DMSO, which diffuses into the plastics material during treatment and is anchored therein. The surface treated may be sensitized with a different metal salt, such as AgNo.sub.3, under reducing conditions, so that a metallic layer of the latter metal is deposited. The treatment bath must be renewed as it is depleted and the silver tends to plate on the process equipment, causing a very untidy condition.
U.S. Pat. No. 4,459,330 discloses a wet process for plating a main group metal on aromatic polymers by the use of a non-aqueous solution of a salt of an alkali metal in a positive valency state and a main group metal in a negative valency state, for example K.sub.4 Sn.sub.9. Metal plating is accomplished by immersion of the polymer into the solution followed by washing with toluene.
An article in The Journal of Vacuum Science and Technology, Vol. 9, No. 1, pp. 354-6 describes the preparation of intermetallic compounds, specifically of niobium and tin, Nb.sub.3 Sn, by coevaporation of two metals onto a rotating surface. A plurality of successive thin layers each of the thickness of approximately one lattice constant should be deposited for properly producing the intermetallic compound, which finally is collected from the carrying surface.
Other current techniques, such as vacuum metallizing and cathode sputtering, are available (Modern Plastics Encyclopedia 1983-1984, p. 358-374), but are not always useful.
In view of the increasing need for plated polymeric articles it will be clear that there is still a great demand for such a simple method providing an adhering interface between a polymeric material and a metallic or psuedo-metallic layer, that will be less cumbersome and complicated than the prior art methods discussed above.
The present invention thus has for its primary objectives the providing of a relatively simple method for metallizing polymeric materials as well as the obtaining of a novel metallized polymer composition.